(a) Field of the Invention
The present invention relates to a method and a system for controlling an output of a starter generator in a hybrid electric vehicle. More particularly, the present invention relates to a method and a system for controlling an output of a starter generator, which may improve noise, vibration, and harshness (NVH) performance, prevent additional cost for the improvement of the NVH performance, and reduce the size and weight of the hybrid starter generator (HSG).
(b) Description of Related Art
Hybrid vehicles use two kinds of power sources efficiently combined to drive a vehicle. Many hybrid vehicles may be driven by an engine utilizing a rotary force by burning fuel (fossil fuel such as gasoline and diesel) and an electric motor utilizing a rotary force by a battery power, which are typically called hybrid electric vehicles (HEV).
The hybrid vehicles may be considered future vehicles that may facilitate the improvement of the fuel efficiency and the reduction of exhaust gases by utilizing the electric motor as an auxiliary power source in addition to the engine. Many studies are currently being conducted to meet the current demands for improving fuel efficiency and developing environmentally friendly products.
The hybrid vehicles may be driven by an electric vehicle (EV) mode that is a pure electric vehicle mode in which only the power of the electric motor (drive motor) is used. Alternatively, hybrid vehicles may be driven by a hybrid electric vehicle (HEV) mode in which the rotary force of the drive motor is used as an auxiliary power while the rotary force of the engine is used as a main power. Additionally, a regenerative braking (RB) mode may be used in which the braking and inertial energy during driving of a vehicle may be collected and charged in a battery through generation of the drive motor.
Thus, the mechanical energy of the engine and the electrical energy of the battery are used together, and the optimal operation range of the engine and the drive motor may be used. In addition, energy may be collected in the drive motor upon braking. Accordingly, an improvement of the fuel efficiency of a vehicle and energy efficiency may be possible.
FIG. 1 is an exemplary view illustrating a configuration of a hybrid system, according to an exemplary embodiment of the present invention. As shown in FIG. 1, the hybrid system for driving a hybrid vehicle may have a layout in which an engine 10, a drive motor 20, and a transmission 30 are arranged adjacent to one another. Furthermore, the engine 10 and the drive motor 20 are connected to transmit power via an engine clutch 50. Additionally, the drive motor 20 and the transmission 30 are directly connected.
Moreover, a hybrid starter generator 40 that may provide a rotary force to the engine 10 (e.g., outputs a cranking torque) upon start-up is connected to the engine 10. In this configuration, when the engine clutch 50 is engaged, a drive shaft of the vehicle may be driven by the drive motor 20. When the engine clutch 50 is disengaged, the drive shaft of the vehicle may be driven by the engine 10 and the drive motor 20.
Additionally, a hybrid power control unit (HPCU) 61 and a low voltage DC/DC converter (LDC) 63 are provided as electric power components. The HPCU 61, which is an integrated control unit, may perform various functions such as selecting the engine 10 or the drive motor 20 as the power for driving the vehicle; determining the power distribution ratio according to the driving condition of a vehicle; converting a voltage of a high voltage battery (HV BATT) 62 into a voltage for the driving of the drive motor; and an MCU (including an inverter) function of controlling the drive motor 20. The LDC 63 may lower a high voltage of the HV BATT 62 to a low voltage to supply the low voltage to the electric components of a vehicle via a low voltage battery (12V BATT) 64. In addition, an electric oil pump 65 is provided.
FIG. 2 is an exemplary view illustrating an exemplary HSG of a hybrid system, according to an exemplary embodiment of the present invention.
A HSG 40 is a core component of a hybrid vehicle for engine start-up and continuous power generation function. The power generation function for charging the high voltage battery 62 may require a wide range of output (e.g., from DC 2 to 8 kW) according to the driving mode of a vehicle. However, to configure the HSG 40 to meet the maximum generation output, a water cooling structure for cooling upon heating may be enlarged. In addition, since the heat-resistance grade of a coil increases, the material cost may excessively increase. Accordingly, recently developed HSGs are configured with devices that may not produce the maximum generation output required for vehicle mode. If necessary, the engine idle rpm may be variably controlled (e.g., 1,300 idle rpm and DC 5 kW are changed into 1,700 idle rpm and DC 8 kW) to compensate for a deficient generation output. However, the variable control of the idle rpm may cause interior noise and vibration due to the increase of the idle rpm, and thus additional noise-proof and vibration-proof measures may be needed.
In the variable control of the idle rpm, the charging capacity of the battery of the HSG may increase due to the increase of the engine idle rpm, whereas the peripheral components (engine) may vibrate during idle speed, deteriorating the NVH performance. To prevent deterioration of the NVH performance, the reinforcement of the housing stiffness of HSG and the rotor skew may be implemented, however this method may increase the manufacturing cost, the size and the weight of the HSG.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.